Use even rounding for better results when converting from scalar to fdot6

src/core/SkEdge.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkEdge_DEFINED
@@ skipping 71 matching lines @@
     SkFixed fCLastX, fCLastY;
 
     int setCubic(const SkPoint pts[4], const SkIRect* clip, int shiftUp);
     int updateCubic();
 };
 
 int SkEdge::setLine(const SkPoint& p0, const SkPoint& p1, int shift) {
     SkFDot6 x0, y0, x1, y1;
 
     {
+#ifdef SK_RASTERIZE_EVEN_ROUNDING
+        x0 = SkScalarRoundToFDot6(p0.fX, shift);
+        y0 = SkScalarRoundToFDot6(p0.fY, shift);
+        x1 = SkScalarRoundToFDot6(p1.fX, shift);
+        y1 = SkScalarRoundToFDot6(p1.fY, shift);
+#else
         float scale = float(1 << (shift + 6));
         x0 = int(p0.fX * scale);
         y0 = int(p0.fY * scale);
         x1 = int(p1.fX * scale);
         y1 = int(p1.fY * scale);
+#endif
     }
 
     int winding = 1;
 
     if (y0 > y1) {
         SkTSwap(x0, x1);
         SkTSwap(y0, y1);
         winding = -1;
     }
 
@@ skipping 13 matching lines @@
     fFirstY     = top;
     fLastY      = bot - 1;
     fCurveCount = 0;
     fWinding    = SkToS8(winding);
     fCurveShift = 0;
     return 1;
 }
 
 
 #endif